Combining Textures with baking
hello is so easy just follow this steps:
1- add a mix node for your images you want to mix, and plug it to principled shader.
2- set the render sampling to 1 , and tile size to the size of your image.
3- set the bake option to diffuse, and uncheck direct and indirect, and choose a margin size (i recommend 1024px= 4px, 2048 px = 8 px, 4096px = 16px).
4- and then bake your image it should take a few seconds...also if your textures/materials are not in the same uv map it wont bake properly...